Spinal implant

ABSTRACT

A spinal cage implant ( 1 ) is adapted to be inserted in a damaged intervertebral disc for restoring the discal height and permitting an arthoesis. Implant ( 1 ) comprises a central part ( 3   c ) with walls ( 4 ) and terminal parts ( 5, 6 ) for bearing against the cortical bone ( 14 ) of the vertebral end plates ( 15, 16 ). Central part ( 3   c ) is adapted to penetrate the vertebral end plates ( 15, 16 ) and transversely projects from the terminal bearing parts ( 5, 6 ). Implant ( 1 ) bears against the vertebral end plates ( 15, 16 ) with terminal parts ( 5, 6 ) and contains bone graft material between walls ( 4 ) which penetrate the openings ( 19, 21 ) in the end plates ( 15, 16 ) and permit bone fusion between the two vertebrae (V 1 , V 2 ). Implant ( 1 ) permits restoring the physiological lordosis and the intervertebral height

TECHNICAL FIELD

The present invention relates to spinal implant devices and associatedtechniques for promoting fusion of two or more vertebrae.

BACKGROUND

It is known that when an intervertebral disc degenerates or is damaged,there is often a compression of the disc and a reduction in the normalintervertebral height. Typically, this condition results in abnormalmotions that become a source of pain.

In order to treat a pathology of this type, the disc is often stabilizedto eliminate the abnormal motions caused by disc disorders or injuries.Generally, one approach is to prevent articulation between the twovertebrae situated on each side of the damaged disc by bone fusion. Thisfusion fixes the vertebrae to each other, eliminating the relativemobility causing the pain.

Various spinal implants to promote fusion between adjacent vertebraehave been proposed. It has been proposed to interconnect the twovertebrae by a kind of rigid U-shaped stirrup which restores the discalheight with a bone graft material disposed inside the stirrup. However,one drawback of this proposal is its diminishing effectiveness over aperiod of time.

An spinal cage is also known which consists of a cylindrical memberprovided with a series of openings and provided with anchoring points.This implant is placed in a recess formed in the intervertebral disc andpenetrates the opposite cortical plates of the two vertebrae which werepreviously hollowed out to receive the implant. This penetration formsopenings in the sub-chondral plates to place spongy bone of thevertebrae in contact with bone graft material placed inside the implant,facilitating bone fusion. U.S. Pat. No. 5,015,247 provides one exampleof this approach.

FR 2,736,538 discloses an intersomatic cage formed by a body havinginclined upper and lower surfaces and parallel lateral walls, providedat their end portions with anti-backward movement teeth. In such astructure the central and end surfaces are in the same plane so that themajor part of the bearing surface is provided by the central part, thatis in contact with the spongy bone, of which the strength is lower thanthe strength of cortical plates. Hence such structure is not entirelysatisfying.

Proper performance of a spinal implant of this type requires balancingthe need to promote fusion between the spongy bone and the need to forma reliable load bearing relationship with the stronger cortical bone. Asa result, the spinal cage must be neither engaged too far into theopenings provided in the cortical plates to provide a sufficiently denseload bearing surface, nor insufficiently inserted, in which case thebone fusion between the two vertebrae would be adversely affected by apoor anchorage. Thus, there is a demand for devices and techniques thatfacilitate attaining the proper balance between fusion and load support.

The present invention meets this demand and provides other significantbenefits and advantages.

DISCLOSURE OF THE INVENTION

The present invention relates to spinal fusion implants and techniques.Various aspects of the present invention are novel, nonobvious, andprovide various advantages. While the actual nature of the inventioncovered herein can only be determined with reference to the claimsappended hereto, certain forms which are characteristic of the preferredembodiments disclosed herein are described briefly as follows.

According to one form of the invention, the spinal implant comprises abody having a central part arranged to allow arthrodesis and at leastone terminal part for bearing against the cortical bone of the vertebralend plates. The central part is adapted to penetrate the vertebral endplates, transversely projecting from the terminal bearing part. Thus theinvention achieves a separation between the end parts constituting theload bearers, and the intermediate part of the implant which permitsfusion. In addition, the central part may include at least one cavityfor receiving a bone graft material.

In another form of the present invention, an implant for insertionbetween a first vertebra having a first cortical bone plate and a secondvertebra having a second cortical bone plate includes two terminalparts. The first terminal part defines a first bearing surface to bearagainst the first cortical bone plate and a second bearing surfaceopposite the first surface to bear against the second cortical boneplate. The second terminal part opposes the first terminal part anddefines a third bearing surface to bear against the first cortical boneplate and a fourth bearing surface opposite the third surface to bearagainst the second cortical bone plate. The implant has an elongatedcentral part defining an upper projection extending past the first andthird surfaces, and a lower projection extending past the second andfourth surfaces. These projections correspondingly pass through openingsin the first and second cortical bone plates when the first and thirdsurfaces bear against the first cortical bone plate and the second andfourth surfaces bear against the second cortical bone plate. Theterminal parts are dimensioned to facilitate restoration of the naturalgeometry of the intervertebral space (lordosis, cyphosis, and paralleldiscs). Thus, the first and second surfaces may be separated by a firstdistance, and the third and fourth surface may be separated by a seconddistance greater than the first distance to accommodate a naturalcurvature of the spine.

In a further form of the present invention, an implant with two terminalparts also has an elongated central part that includes a pair oflongitudinal walls defining a cavity. The walls define a first edgeprojecting past the first and third surfaces and a second edgeprojecting past the second and fourth surfaces. The first and secondedges correspondingly penetrate the first and second cortical boneplates when the first and third surfaces bear against the first corticalbone plate and the second and fourth surfaces bear against the secondcortical bone plate.

According to another form, the bearing surfaces of the terminal endparts are defined by flanges extending from opposing ends of the implantalong its longitudinal axis. Preferably, the bearing surfaces aregenerally flat for bearing against the cortical bone of the vertebralend plates of the two adjacent vertebrae. It is also preferred thatopenings be cut into the cortical plates in their central regionscorresponding to the length of a central part of the implant along thelongitudinal axis and leaving a region of the cortical bone platesaround the periphery of the openings. The length of the remainingperipheral plate corresponds to the length of the bearing surfaces alongthe longitudinal axis. When the implant is placed in position, the edgesof the walls of the central part engage the openings cut in the corticalplates and consequently do not substantially bear against the remainingperipheral portion of the plates. A cavity may be defined by the centralpart that holds bone graft material in contact with the spongy bone ofthe two vertebrae. In contrast, the bearing surfaces of the flanges aredisposed adjacent the edges of the openings of the cortical plates andbear against the remaining portions of the plates to establish a strongload bearing relationship. Thus, both bone fusion and support aredistinctly accommodated by different parts of the implant structure,which permits obtaining a satisfactory support of the vertebral bodieson the implant and an excellent arthrodesis.

Yet another form of the present invention includes a cutting toolaccessory to prepare the cortical plates of two adjacent vertebrae forinsertion of an implant. This tool comprises a proximal handle connectedto an elongate shaft configured to rotate about a longitudinal axis ofthe tool. The tool also includes a first non-cutting portion with theshaft extending therethrough and being configured to rotate relativethereto. A cutting portion is fixed to the shaft to rotate therewith andis positioned distal to the first non-cutting portion. The cuttingportion includes a first pair of generally parallel opposing faces and asecond pair of opposing faces each extending between the first pair offaces. The second pair of faces each define a number of cutting teeth. Asecond non-cutting portion is fixed to the cutting portion that includesa distal head. The first non-cutting portion, the cutting portion, andthe second non-cutting portion have a rotatably selectable alignmentthat presents a generally constant height corresponding to theintersomatic space defined between the cortical bone plates tofacilitate insertion therein. Once inserted, the cutting portion may berotated out of this alignment to cut a first opening in the firstcortical bone plate and a second opening into the second cortical boneplate. The cutting portion and to non-cutting portions may be arrangedto provide uniform, symmetrical cutting of these openings with apredetermined length corresponding to the dimensions of a given implantdevice.

In an additional form, a technique of spinal fixation includes cuttingadjacent vertebrae and inserting an implant therebetween to promotefusion and provide suitable support. The implant may be inserted byanterior or posterior surgical approaches. The cutting may be performedby the cutting tool of the present invention and may include initiallyinserting the tool so that a first pair of faces are in contact with arespective one of the first and second cortical bone plates, turning ahandle to rotate the cutting portion to remove cortical bone withcutting teeth defined by a second pair of faces, and withdrawing thetool. The tool may be used to form openings readily positioned in thecentral region of the adjacent vertebrae that leaves cortical bone plateabout the openings. The insertion of the implant may include positioningthe implant of the present invention between the first and secondvertebrae and turning the implant about one quarter of a turn.

It is envisioned that the implants of the present invention may be usedwith other tools and procedures, that the tools of the present inventionmay be used with other implants and procedures, and that the proceduresof the present invention may be used with other implants and tools aswould occur to those skilled in the art without departing from thespirit of the present invention.

Accordingly, one object of the invention is to provide a spinal implantarranged to facilitate proper fusion of two or more vertebrae. Theimplant may be arranged to have at least one structural part to promotebone fusion through contact with spongy vertebral bone and one or moreother structural parts adapted for contact with cortical bone to provideload support.

Another object is to provide a tool accessory to facilitate implantationof devices suitable to promote fusion.

Still another object is to provide a technique for preparing a sitebetween two vertebrae to be fused and inserting an implant.

Other objects, features, benefits, forms, aspects, and advantages of thepresent invention will become apparent from the description and drawingsherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, to a larger scale, of one embodiment of aspinal implant of the present invention.

FIG. 2 is a perspective view of one embodiment of a cutting tool of thepresent invention for mounting the implant of FIG. 1.

FIG. 3 is a perspective view of a distracting wedge or “distractor” usedfor carrying out a surgical method in accordance with the presentinvention.

FIG. 4 is a partial elevational view diagrammatically illustrating theinsertion of the cutting tool between two vertebrae.

FIG. 5 is a partial elevation view showing the cutting tool afterrotation of the cutting portion through 90° and penetrating the corticalplates of the two adjacent vertebrae.

FIG. 6 is a partial sectional view taken in a sagittal plane showing theimplant of FIG. 1 positioned in an intervertebral disc for achieving aspinal fusion.

FIG. 7 is a perspective view of a spinal segment in the intervertebraldisc in which two implants have been installed.

MODE(S) FOR CARRYING OUT THE INVENTION

For the purpose of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended. Any alterations and further modificationsin the described device, and any further applications of the principlesof the invention as described herein are contemplated as would normallyoccur to one skilled in the art to which the invention relates.

FIGS. 1, 6, and 7 depict spinal cage implant 1. Implant 1 is adapted tobe inserted in a cavity provided in a damaged intervertebral disc 2(FIG. 7), so as to restore the normal height of the intervertebral spacebetween the two vertebrae V1 and V2 adjacent to the disc 2, for examplethe lumbar vertebrae L3, L4 as depicted in FIG. 7. FIG. 1 shows implant1 disposed along its longitudinal axis YY. Implant 1 comprises a hollowbody 3 of elongate shape, having a central part 3 c formed by twoparallel longitudinal walls 4 arranged to permit the arthrodesis and, atthe two opposite ends of the central part 3 c, in the direction of theimplantation of the implant 1, two terminal parts 5, 6 for bearingagainst the cortical bone 14 of vertebral cortical bone plates 15, 16 ofthe two vertebrae (V1, V2) adjacent to the disc 2 (see, for example,FIG. 6).

The longitudinal walls 4 define therebetween a cavity 7 and are providedwith openings 11. Terminal parts 5, 6 are disposed opposite each otheralong axis YY and each include a terminal face defining a centrallylocated threaded hole 11 a. Holes 11 a are configured for engagement bya threaded shaft of an insertion/manipulation accessory (no shown) tofacilitate placement of implant 1 between vertebrae V1, V2. The cavity 7is provided to receive a graft G of spongy bone or any other materialfavoring bone fusion, for example a synthetic ceramic.

Terminal part 5 has two opposite bearing surfaces 12 transverse to axisYY which are so dimensioned that they are separated by distance d1.Terminal part 6 has two opposite bearing surfaces 13 transverse to axisYY which are so dimensioned that they are separated by distance d2.Distances d1, d2 are adapted to the geometry of the intervertebral spaceto be restored. When d2 is greater than d1 as depicted, implant 1 ispreferred for fusion of vertebrae in a region of the spine having anatural curvature. Distance 1 corresponds to a maximum width dimensionof body 3. In one embodiment, the width of body 3 is generally constantalong axis YY and is about the same as distance d1 to facilitate aproper fit between vertebrae V1, V2 as will become more apparenthereinafter.

The terminal parts 5, 6 are extended by load bearing flanges 8, 9,namely two load bearing flanges 8 for part 5 and two load bearingflanges 9 for part 6. In the depicted embodiment, flanges 8, 9 formparallel bars perpendicular to the longitudinal walls 4, and definegenerally flat surfaces 12, 13 for bearing against the cortical bone 14of the vertebral end plates 15, 16.

In the illustrated embodiment, the longitudinal walls 4 have asubstantially trapezoidal contour of which the small base corresponds tothe terminal part 5 and the large base corresponds to the terminal part6. The walls 4 constituting the central part 3 c of the implant 1 are soshaped as to transversely project from the terminal bearing parts 5, 6,as can be seen in FIGS. 1 and 6. Thus the walls 4 can penetraterespective openings 19, 21 of the vertebral plates 15, 16 whose edgesbear against the bearing surfaces 12, 13 of the flanges 8, 9 (FIG. 6).Flanges 8, 9 are shaped to define step projections 17 a, 18 a to furtherfacilitate penetration of openings 19, 21. Projections 17 a, 18 a alsoprovide a lip to maintain alignment of bearing surfaces 12, 13 withcortical bone plates 15, 16 about the periphery of the openings as shownin FIG. 6. Walls 4 also include tapered edges 4 a to facilitatepenetration. Correspondingly, central part 3 c has upper projection 3 aand lower projection 3 b defined by edges 4 a. Notably, edges 4 a andprojections 3 a, 3 b transversely project away from surfaces 12, 13.

Implant 1 may be placed in position in the intervertebral disc 2 afterpreparation with cutting tool accessory 22 which will now be describedwith reference to FIGS. 2, 4, and 5. Preferably, tool 22 is made from ametallic material suitable for surgical use. Tool 22 has a millingcutter 23 including central cutting portion 24 and two non-cuttingportions 31, 36 arranged at opposite ends of central cutting portion 24.Non-cutting portions 31, 36 have height h corresponding to theintersomatic space and permitting uniform, symmetrical cutting of apredetermined length through a central region of both vertebral plates15, 16. Preferably, the geometry of portions 24, 31, 36 is determinedfor preparing the intersomatic space with the geometry of implant 1 torestore the natural lordosis of the intervertebral space, andcorrespondingly the distances represented by h and d1 are approximatelyequal.

Central cutting portion 24 has a trapezoidal shape with two generallysmooth, longitudinal faces 25 opposed to each other. Faces 25 areconfigured to facilitate insertion into the intersomatic space beinggenerally separated from each other by distance h. Central cuttingportion 24 also has cutting faces 26 extending between faces 25. Cuttingfaces 26 define a number of uniformly spaced apart cutting teeth 28.Teeth 28 each extend along a generally straight path that is slanted atan oblique angle relative to longitudinal axis XX of tool 22.Preferably, central cutting portion 24 is made from a suitable metallicmaterial that has been machined to form teeth 28.

Non-cutting portion 31 is fixed to the distal end of central cuttingportion 24. Portion 31 extends from central cutting portion 24 toprovide a distal head in the form of a parallelepiped-shaped bar.Portion 31 has a first dimension substantially the same as distance h tobe generally coextensive with faces 25 of central cutting portion 24.Portion 31 also has opposing faces 32 separated from each other by adistance H as shown in FIG. 5. Preferably distance H is approximatelyequal to distance d2 when tool 22 is being utilized to install implant1.

Tool 22 also includes a shaft or shank 33 connected to a proximalactuating handle 34. Shank 33 is fixed to central cutting portion 24 andnon-cutting portion 31. Shank 33 extends from the small end face 27remote from the non-cutting head 31 and terminates in the handle 34which permits rotating the cutting portion 24 about the longitudinalaxis XX of tool 22.

Non-cutting portion 36 has a rectangular shape with generally planarfaces 37, 38. Portion 36 may be inserted between two consecutivevertebrae during rotation of central cutting portion 24. Portion 36extends in the direction toward the handle 34 by a tubular part 40 andthrough block 40 a which terminates in the vicinity of the handle 34.Non-cutting portion 36 is provided with lateral stops 39 capable ofbeing put into abutment against the sides of the vertebrae (V1, V2)after insertion therebetween. Non-cutting portion 36 encloses shank 33.Shank 33 is configured to rotate relative to portion 36.Correspondingly, when handle 34 is turned, shank 33, central cuttingportion 24, and non-cutting portion 31 rotate together about axis XXwith non-cutting portion 36 preferably remaining stationary. It shouldbe noted that the partial view of FIGS. 4 and 5 do not show handle 34and depict a cutaway view of non-cutting portion 36 with shank 33projecting therefrom.

Various nonlimiting embodiments of a spinal fixation or fusion procedureof the present invention are next described. One procedure ischaracterized by: (a) cutting the vertebrae V1, V2 and disc 2 with tool22 to prepare for implantation and (b) inserting the implant 1 betweenvertebrae V1, V2. Another more detailed procedure for fusing twovertebrae together is described in terms of procedural stages (a)-(h) asfollows:

(a) A surgeon first separates the dural sleeve forming the extension ofthe bone marrow if the procedure is in the lumbar region and thencarries out a discectomy to provide space for implant 1 in disc 2.

(b) The surgeon inserts between the two vertebrae V1, V2 from the rear(posterior), two lordosis distractors 41 as shown in FIG. 3. Eachdistractor 41 consists of a parallelepiped-shaped part 42 extended by awedge part 43 of triangular section. Part 42 is provided with thrustplate 44. Distractors 42 are inserted laterally with respect to thecavity provided by the discectomy of stage (a). Each distractor 41 isinitially inserted by presenting its narrower aspect between V1 and V2,and, then turned through 90° so as to spread apart the vertebrae andrestore the discal height and the height of the considered vertebralsegment. Next, one of the distractors 41 is removed.

(c) The surgeon inserts tool 22 between the vertebrae V1, V2 as shown inFIG. 4 so that the larger, smooth faces 25 are in contact with thevertebral plates 15, 16. When the cutting portion 24 is correctlypositioned in the central region of the cortical plates, stops 39 comeinto abutment with the outer surface of the vertebrae V1, V2 andnon-cutting portion 36 is partly inserted between the plates 15, 16.

(d) Next, the surgeon turns handle 34, causing cutting portion 24 torotate about axis XX. Typically, portion 24 is rotated a number oftimes. As rotation continues cutting teeth 28 engage the central partsof cortical plates 15, 16 (FIG. 5), gradually removing cortical bone 14.At the end of the hollowing out of these plates, the cutting faces 26 ofthe central cutting portion 24 and the cutting teeth 28 have cut throughthe plates 15, 16 to form generally centrally located openings 19, 21.Remaining portions of plates 15, 16 then bear against the opposite faces32 of non-cutting portion 31 and against non-cutting portion 36.

(e) Then, the surgeon withdraws tool 22 from between vertebrae V1, V2.

(f) Next, the surgeon inserts implant 1, previously filled with the bonegraft G, between the plates 15, 16 from the rear to a suitable positionby presenting the terminal part 6 and the bearing flanges 9 at the frontend. The implant 1 is presented flat, so that longitudinal walls 4 aregenerally parallel to the cortical plates 15, 16 and initially come intocontact therewith during insertion.

(g) Thereafter, the surgeon turns implant 1 through a quarter of a turnabout its longitudinal axis (YY) so as to place it in the position shownin FIG. 6 with walls 4 substantially perpendicular to the corticalplates and its flat surfaces 12, 13 generally parallel to ,corticalplates 15, 16. Implant 1 may be inserted and turned by engaging hole 1la with a correspondingly threaded shaft of an accessory tool (notshown). The edges 4 a of the longitudinal walls 4 which defineprojections 3 a, 3 b are inserted into openings 19, 21 thereby passingthrough plates 15, 16, while remaining portions of plates 15, 16 bearagainst flat surfaces 12, 13. Implant 1 is then in its final position inwhich it is stabilized. The bone graft G is in contact with the spongypart S1, S2, promoting bone fusion.

(h) The surgeon removes the second distractor 41 then repeats thepreceding sequence of stages (a) through (g) to mount a second spinalcage implant 1 by placing it in a position generally parallel to thefirst cage implant 1 on the other side of the axis of the spinal columnresulting in the configuration depicted in FIG. 7 (implants 1 are shownin phantom).

In other embodiments, it is envisioned that the described stages may bealtered, deleted, combined, repeated, or resequenced as would occur tothose skilled in the art. By way of nonlimiting example, the procedureaccording to the present invention may utilize one or more differenttools to prepare the spine for fixation by the implant of the presentinvention. In another example, the tool of the present invention may beutilized to prepare a surgical site for a different implant.

Indeed, the scope of the invention is not intended to be limited to thedescribed embodiment and may also include variants within the scope ofthe accompanying claims. For example, terminal bearing surfaces 12, 13for the vertebral plates may have any shape, such as a curved orcylindrical shape with plates 15, 16 being correspondingly cut so as toallow placing the bearing surfaces in a suitable position. Further,these bearing surfaces may be interconnected in pairs and constitute asingle member 50 as shown in FIG. 6.

Likewise, the central part of the implant of the present invention mayhave any shape, preferably retaining edges that project from theterminal bearing parts. In particular, the body may have a multitude ofcells. Also, it should be generally noted that the implant and tool ofthe present invention may be adapted to a geometry of the spine withrespect to lordosis, cyphosis or parallel vertebral end plates. Thus,the present invention includes application to adjacent vertebrae otherthan L3, L4. Correspondingly, the implant and the cutting portion of thetool may have a different shape, such as a cylindrical geometry otherthan the generally conical geometry depicted. Also, Instead of using thedisclosed implant 1, the spinal space prepared by tool 22 can be filledwith any other material as would occur to those skilled in the art.

According to other embodiments, the implant can be partly or totallyconstituted by porous rehabitable or resorbable materials favoringosteointegration. Such embodiments include: (a) an implant according tothe above-illustrated geometry entirely made of a resorbable orrehabitable material; (b) an implant in which the whole of the centralpart is made of a resorbable or rehabitable material; or (c) an implantin which the periphery of the central part is made of a metallic orother material and the inside part is of a material favoringosteointegration that may be in an initially solid, pasty or liquidstate.

In another alternative embodiment an implant is provided with only onebearing end part in which the end portion opposite to the bearing endpart is open and forms a U shape for receiving a bone graft or arehabitable or resorbable material.

French Patent Application Number 97 10664 filed on Aug. 26, 1997 towhich priority is claimed is hereby incorporated by reference as if itwere specifically set forth in its entirety herein. While the inventionhas been illustrated and described in detail in the drawings andforegoing description, the same is to be considered as illustrative andnot restrictive in character, it being understood that only thepreferred embodiments have been shown and described and that allchanges, modifications, and equivalents that come within the spirit ofthe invention as defined by the following claims are desired to beprotected.

What is claimed is:
 1. An implant for insertion between a first vertebra and a second vertebra, the first vertebra having a first cortical bone plate and the second vertebra having a second cortical bone plate, characterized in that the implant comprises: a first terminal part defining a first bearing surface to bear against the first cortical bone plate, a second bearing surface opposite said first surface to bear against the second cortical bone plate; a second terminal part opposite said first terminal part, said second terminal part defining a third bearing surface to bear against the first cortical bone plate and a fourth bearing surface opposite said third surface to bear against the second cortical bone plate; an elongated central part including a pair of longitudinal walls having a generally trapezoid configuration defining a cavity therebetween each of said walls projecting transversely from the first and second terminal parts and including a tapering edge adapted to penetrate the first and second cortical bone plates, and a projection extending transverse to said walls and positioned between said cavity and said first terminal part, said projection configured to correspondingly penetrate the first or second cortical bone plate when said first and third surfaces bear against the first cortical bone plate and said secondhand fourth surfaces bear against the second cortical bone plate.
 2. The implant of claim 1 comprising a second projection opposite said projection, said second projection extending transverse to said walls and positioned between said cavity and said second terminal part, said projection configured to correspondingly penetrate the first or second cortical bone plate when said first and third surfaces bear against the first cortical bone plate and said second and fourth surfaces bear against the second cortical bone plate.
 3. The implant of claim 1 wherein said first terminal part includes a first flange defining said first surface and a second flange defining said second surface; and said second terminal part includes a third flange defining said third surface and a fourth flange defining said fourth surface.
 4. The implant of claim 1 wherein said first, second, third, and fourth surfaces are generally flat.
 5. The implant of claim 2 wherein the first projection, the second projection and the tapering edges of the longitudinal walls define an opening into the cavity.
 6. An implant for insertion between opposing endplates of adjacent vertebrae, said implant comprising: an elongate body defining a longitudinal axis and having a cavity therein; said body comprising: a first end including a first planar surface and an opposite second planar surface, said first and second planer surfaces configured to engage with the opposing endplates of the adjacent vertebrae; a second end including a third planar surface and an opposite fourth planar surface, said third and fourth planer surfaces configured to engage with the opposing endplates of the adjacent vertebrae; first and second longitudinal walls extending from the first end to the second end, each of said first and second walls having a first tapering edge and an opposite second tapering edge wherein the first and second edges are configured to penetrate the opposing endplates of the adjacent vertebrae; a first projection extending from the first planar surface in a direction generally transverse to the longitudinal axis, said first projection positioned adjacent the cavity, disposed between the first and second longitudinal walls, and configured to penetrate one of the adjacent vertebrae, and a third projection extending from the third planar surface in a direction generally transverse to the longitudinal axis, said third projection positioned adjacent the cavity, disposed between the first and second longitudinal walls and configured to penetrate one of the adjacent vertebrae.
 7. The implant of claim 6 comprising: a second projection extending from the second planar surface in a direction generally transverse to the longitudinal axis and opposite said first projection; and, a fourth projection extending from the fourth planar surface in a direction generally transverse to the longitudinal axis and opposite said third projection.
 8. The implant of claim 6 wherein the first tapering edges of the first and second longitudinal walls, the first projection, and the third projection define an opening into the cavity.
 9. The implant of claim 6 wherein at least a portion of the implant is composed of a resorbable material.
 10. The implant of claim 6 comprising a flange extending from the first end.
 11. The implant of claim 10 comprising a flange extending from the second end.
 12. The implant of claim 6 comprising a first opening and an opposite, second opening into the cavity to define a passageway through the implant in a direction traverse to the longitudinal axis.
 13. The implant of claim 12 comprising a bone graft material in the cavity to contact spongy bone of the opposing vertebrae.
 14. The implant of claim 1 wherein the tapering edge of each of the longitudinal walls extends in a longitudinal direction.
 15. The implant of claim 1, wherein said walls each have a generally trapezoidal contour.
 16. The implant of claim 1, wherein said cavity holds bone graft material.
 17. The implant of claim 1, wherein at least a portion of the implant is composed of a porous material.
 18. The implant of claim 1, wherein said first and second surfaces are separated by a first distance and said third and fourth surfaces are separated by a second distance greater than said first distance to accommodate a spinal curvature. 